Introduce server query padding

For compatibility with security patches to future game servers versions
this adds a 1200 byte padding to all requests packets as defined in the
following HLDS mailing list post:

https://www.mail-archive.com/[email protected]/msg01194.html

See koraktor/steam-condenser#331

src/main/java/com/github/koraktor/steamcondenser/steam/packets/A2S_INFO_Packet.java

@@ -1,8 +1,8 @@
-/**
+/*
  * This code is free software; you can redistribute it and/or modify it under
  * the terms of the new BSD License.
  *
- * Copyright (c) 2008-2011, Sebastian Staudt
+ * Copyright (c) 2008-2020, Sebastian Staudt
  */
 
 package com.github.koraktor.steamcondenser.steam.packets;
@@ -13,7 +13,7 @@
  * @author Sebastian Staudt
  * @see com.github.koraktor.steamcondenser.steam.servers.GameServer#updateServerInfo
  */
-public class A2S_INFO_Packet extends SteamPacket {
+public class A2S_INFO_Packet extends QueryPacket {
 
     /**
      * Creates a new A2S_INFO request object

src/main/java/com/github/koraktor/steamcondenser/steam/packets/A2S_PLAYER_Packet.java

@@ -1,8 +1,8 @@
-/**
+/*
  * This code is free software; you can redistribute it and/or modify it under
  * the terms of the new BSD License.
  *
- * Copyright (c) 2008-2012, Sebastian Staudt
+ * Copyright (c) 2008-2020, Sebastian Staudt
  */
 
 package com.github.koraktor.steamcondenser.steam.packets;
@@ -20,7 +20,7 @@
  * @author Sebastian Staudt
  * @see com.github.koraktor.steamcondenser.steam.servers.GameServer#updatePlayers
  */
-public class A2S_PLAYER_Packet extends SteamPacket {
+public class A2S_PLAYER_Packet extends QueryPacket {
 
     /**
      * Creates a new A2S_PLAYER request object without a challenge number

src/main/java/com/github/koraktor/steamcondenser/steam/packets/A2S_RULES_Packet.java

@@ -1,8 +1,8 @@
-/**
+/*
  * This code is free software; you can redistribute it and/or modify it under
  * the terms of the new BSD License.
  *
- * Copyright (c) 2008-2011, Sebastian Staudt
+ * Copyright (c) 2008-2020, Sebastian Staudt
  */
 
 package com.github.koraktor.steamcondenser.steam.packets;
@@ -21,7 +21,7 @@
  * @author Sebastian Staudt
  * @see com.github.koraktor.steamcondenser.steam.servers.GameServer#updateRules
  */
-public class A2S_RULES_Packet extends SteamPacket {
+public class A2S_RULES_Packet extends QueryPacket {
 
     /**
      * Creates a new A2S_RULES request object including the challenge number

src/main/java/com/github/koraktor/steamcondenser/steam/packets/QueryPacket.java

@@ -0,0 +1,43 @@
+/*
+ * This code is free software; you can redistribute it and/or modify it under
+ * the terms of the new BSD License.
+ *
+ * Copyright (c) 2020, Sebastian Staudt
+ */
+
+package com.github.koraktor.steamcondenser.steam.packets;
+
+import java.util.Arrays;
+
+import org.apache.commons.lang3.ArrayUtils;
+
+/**
+ * This is used as a wrapper to create padding of request packets to a minimum
+ * size of 1200 bytes. This was introduced in November 2020 as a
+ * counter-measure to DoS attacks on game servers.
+ *
+ * @author Sebastian Staudt
+ */
+class QueryPacket extends SteamPacket {
+
+    // The minimum package size as defined by Valve
+    private static final int STEAM_GAMESERVER_MIN_CONNECTIONLESS_PACKET_SIZE = 1200;
+
+    static byte[] addPadding(byte[] data) {
+        if (data.length < STEAM_GAMESERVER_MIN_CONNECTIONLESS_PACKET_SIZE - 5) {
+            byte[] padding = new byte[STEAM_GAMESERVER_MIN_CONNECTIONLESS_PACKET_SIZE - 5 - data.length];
+            return ArrayUtils.addAll(data, padding);
+        } else {
+            return data;
+        }
+    }
+
+    /**
+     * Creates a new query packet including data padding
+     *
+     * @param data The data of the original query
+     */
+    QueryPacket(byte header, byte[] data) {
+        super(header, addPadding(data));
+    }
+}

src/test/java/com/github/koraktor/steamcondenser/steam/packets/QueryPacketTest.java

@@ -0,0 +1,44 @@
+/*
+ * This code is free software; you can redistribute it and/or modify it under
+ * the terms of the new BSD License.
+ *
+ * Copyright (c) 2020, Sebastian Staudt
+ */
+
+package com.github.koraktor.steamcondenser.steam.packets;
+
+import java.util.Arrays;
+
+import org.apache.commons.lang3.ArrayUtils;
+
+import org.junit.Test;
+
+import static org.hamcrest.MatcherAssert.*;
+import static org.hamcrest.core.Is.*;
+import static org.hamcrest.core.IsEqual.*;
+
+public class QueryPacketTest {
+
+    @Test
+    public void testPadding() {
+        QueryPacket packet = new QueryPacket((byte) 0x21, new byte[] { 0x22, 0x23, 0x24, 0x25 });
+        byte[] bytes = packet.getBytes();
+
+        assertThat(bytes.length, is(1200));
+
+        assertThat(bytes[0], is((byte) 0xFF));
+        assertThat(bytes[1], is((byte) 0xFF));
+        assertThat(bytes[2], is((byte) 0xFF));
+        assertThat(bytes[3], is((byte) 0xFF));
+        assertThat(bytes[4], is((byte) 0x21));
+        assertThat(bytes[5], is((byte) 0x22));
+        assertThat(bytes[6], is((byte) 0x23));
+        assertThat(bytes[7], is((byte) 0x24));
+        assertThat(bytes[8], is((byte) 0x25));
+
+        byte[] paddingBytes = ArrayUtils.subarray(bytes, 9, 1200);
+        byte[] expectedPadding = new byte[1191];
+        Arrays.fill(expectedPadding, (byte) 0x0);
+        assertThat(paddingBytes, is(equalTo(expectedPadding)));
+    }
+}